Since changes occur in the virus maturation cycle which allows cells to become chronically infected rather than be destroyed lytically, this study will investigate the possible differences in proteins and nucleic acids associated with SSPE (chronic), SSPE lytic, and "normal" measles infections. Techniques will be utilized to isolate and identify not only the native (-) strand of ribonucleic acid, but also the m RNA transcribed in vivo. Hybridization of the infectious RNA of SSPE and measles to their corresponding messenger RNA''s and to others will relate the percent of homology which exists between these disease associated virions. Differences in sizes of the RNA's could possibly identify areas on the genome coding for the final maturation function of a lytic virus. Comparison of proteins isolated from both in vivo and in vitro systems may also, in fact, determine in which category the virus will function. Infected cells lacking a specific viral glycoprotein may not be able to bud mature virions from the membrane.